1. Field of the Invention
This invention relates generally to fiber-reinforced polymer composites, preferably containing natural fibers, more preferably coconut coir fibers.
2. Description of Related Art
Fiber-reinforced polymer composites containing synthetic or natural fibers have been used as construction materials in the past. Plastics reinforced with synthetic fibers possess high strength, but are expensive to produce. Unlike synthetic fibers, natural fibers are readily available. However, natural fibers are hydrophilic, which causes them to be incompatible with many hydrophobic polymers, including polyvinyl chloride (PVC) and polyolefins.
Coir is a natural fiber obtained from coconut husks. Coir fibers are strong, lightweight, and abundant. In the past, coir fibers have been used as reinforcement in polymeric composite materials. However, raw coir is normally hydrophilic, rendering them incompatible with polyolefins and PVC. Specifically, raw coir as used in the prior art include coir fibers and coconut pith. While coir fibers are comparatively hydrophobic, pith is very hydrophilic and is incompatible with polyolefins and PVC. Complete separation of coir and pith by physical processes has not been achieved in the prior art.
To overcome incompatibility between coir and a polymer matrix, coir-reinforced composites have been made using hydrophilic resins, including epoxy resins and polyurethanes. In many cases, epoxy resins and polyurethanes have reactive sites, such as epoxide or isocyanate functionalities, which can react with hydrophilic sites on the coir fibers.
Composites made from hydrophilic fibers and/or polymers present the difficulty that they have a tendency to absorb water, rendering them unsuitable for use in outdoor construction. Attempts to overcome this have been made by using polyolefins as matrix polymers in coir-reinforced materials. However, since coir used in the past is hydrophilic, this material has been found to be incompatible with hydrophobic polymers. As a result, coir-reinforced polyolefin composites of the prior art use chemically modified coir. Coir, as used in these composites, has been modified to incorporate hydrophobic groups into the coir structure, increasing compatibility between the coir and the polyolefin.
The current disclosure relates to fiber-reinforced polymer composites containing natural coir fibers and a hydrophobic matrix polymer. Compatibility between the coir fibers and the hydrophobic matrix polymer is increased without requiring chemical modification of the fibers.